<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .green {
            background-color: lawngreen;
        }
    </style>
</head>
<body>
    <div class="the_div">
        <p>我是p标签</p>
        <h3>我是h3</h3>
        <h3>我是h3</h3>
        <h3>我是h3</h3>
        <a id="theA" href="#">我是一个a标签</a>
        <ul>
            <li>北京</li>
            <li>天津</li>
            <li>南京</li>
        </ul>
        <ol class="my_li">
            <li>大张</li>
            <li>大王</li>
            <li>大狗</li>
        </ol>
        <ul class="my_li">
            <li>小明</li>
            <li>小红</li>
            <li>小蓝</li>
        </ul>
    </div>

    <script>
        const a = document.querySelector('.the_div #theA');
        const h3 = document.querySelectorAll('.the_div h3');
        const lis = document.querySelectorAll('li');
        const xli = document.querySelectorAll('ul.my_li li');
        const xlix = document.querySelector('ul.my_li li:nth-child(2)');
        const tli = document.querySelector('ul li:nth-child(2)');
        console.log(h3);
        xlix.innerText = '小六'
        xlix.style.color = 'red'
        tli.classList.add('green')
        
    </script>
</body>
</html>